The two intestinal enzymes, alkaline phosphatase and 5'-nucleotide phosphodiesterase, have many physical properties in common; we are now prepared to examine their mechanistic and structural similarities. Major emphasis will be given to the isolation of an expected covalent enzyme-substrate intermediate of the phosphodiesterase. If found, it will be characterized chemically and compared to the previously known intermediate of the alkaline phosphatase. If no covalent intermediate is found, the active site will be affinity labelled for characterization. The metal ion content of the phosphodiesterase will be determined, the apoenzyme prepared, and the effects of various metal ions on it examined. The research also involves considerable synthetic organic chemistry; compounds prepared include modified nuclectides, phosphonate and phosphonothioate monoesters, some of them radioactive, to be used as substrates, inhibitors, and ligands for affinity chromatography. BIBLIOGRAPHIC REFERENCE: Enzymic Hydrolysis of Phosphonate Esters. Reaction Mechanism of Bovine 5'-Nucleotide Phosphodiesterase, S. J. Kelly and L. G. Butler, Biochemistry, 16, 1102 (1977).